Generally, I have no trouble tracking calories and nutrients I consume thanks to MyFitnessPal, which is a neat little application (Android/ iOS/ web) that basically does everything for you. It’s powered by an absolutely enormous food database. All that’s required of the user is to search for a food, enter the number of servings and submit. The process takes all of two or three seconds once you get into the swing of things. It’s easy enough to track the consumption of discrete food items, like grilled chicken breast or a tablespoon of coconut oil or 200g of sweet potato (so long as you have a food scale or are good at estimating). But things can get tricky when attempting to calculate the number of calories and nutrients in a recipe and even trickier when calculating the portion size of that recipe you might have consumed.

For example, I might make a huge pot of stew, then eat a bowlful of it, but how do I know how much I’ve consumed? Well, for one, I could measure out a couple of cupfuls of stew into my bowl, but how do I know how many calories and macros are in those two cups? I’d need to know two other things: 1) how many calories and macros the whole pot contained, and 2) how many cups of stew are in the pot. That second part is actually a lot trickier than it sounds, especially when it’s a huge, hot pot of stew that I might not be inclined to measure out cup-by-cup into another pot to determine how many cups I’m starting with. So what to do? Here’s the process I follow; although it might seem complicated on first read, I promise it’s not in practice:

1. MyFitnessPal includes a function that allows recipes to be created that are comprised of multiple food items. It also requires the user to enter the number of servings the recipe makes. Since I never know this (I make up recipes as I go), I always tell the app that it makes ONE serving. I’ll explain why in a minute. I then weigh out all the items in the recipe and enter them into the app. Once the recipe is created, the app generates a nutrition table for it that lists calories, macros and some vitamins/ minerals. Since I’ve indicated that the whole pot is a single serving, the table might show me something like “5,387 calories per serving.”
   

   A recipe profile in MyFitnessPal. Note that I have this set as a single serving.

2. Now I have to figure out how many cups are in the pot of stew. I could, of course just estimate. If I know my pot holds eight quarts I can come up with a reasonable estimate. But sometimes reasonable isn’t good enough, especially if what I’ve made is very energy dense. If I’m off by a few cups (which is likely), that can significantly throw off my individual serving calculations. To get an accurate answer, I first measure the depth of the food in the pot with a ruler (either on the inside with a plastic ruler I’d only use for this or on the outside of the pot). Say it’s six inches deep. Then I measure the interior diameter of the pot; say that’s nine inches. Since the pot is a cylinder, then so is the stew inside it. So now I know I have a cylinder of stew that six inches high by nine inches in diameter.
3. Now all I have to do is calculate the volume of the stew cylinder. There are lots of online utilities that can do this, but I use Wolfram Alpha for virtually every mathematical calculation I have to perform in personal and professional life. You can enter what you want calculated in plain English, so I enter “number of cups in a cylinder 5.5 inches tall by 9 inches diameter.” Boom. Done. It tells me there are 6.06 quarts or just over 24 cups in my stew cylinder.
   

   Wolfram Alpha comes in very handy for stuff like determining the volume of a stew cylinder.

   

   This is the conversion table generated by Wolfram Alpha.

4. Remember how I told MyFitnessPal that the pot of stew was one serving? This step is where it comes in handy. I can now make my serving size whatever I want. So if I want the pot to be 10 servings, I know that’s 2.4 cups (24/10). Now I can scoop 2.4 cups into my bowl and log it in MyFitnessPal by selecting the recipe and entering a fractional serving size, i.e. 0.1 servings since I’m eating a tenth of the pot. All my nutrients are calculated and added right to my daily totals. If I want to only have a cup of the stew, I simply divide 1 by 24 and get ~0.042, so that would be the serving size I enter into the application.

Determining the correct calories could also be accomplished by weighing the empty pot on a food scale, and then weighing it again once full of cooked food and logging the difference. Then you’d weigh the portion you wanted to eat and convert it into a fraction of the whole and enter it into MyFitnessPal as described in #4 above. The problem is that 1) my food scale maxes out at 5.5 lbs. and most of the stuff I cook plus the cookware is much heavier than that, and 2) the hot pot might melt the surface of the scale (mine is plastic).